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    <title>Document</title>
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<body>
    <ul id="parent-list">
        <li id="post-1">Item 1</li>
        <li id="post-2">Item 2</li>
        <li id="post-3">Item 3</li>
        <li id="post-4">Item 4</li>
        <li id="post-5">Item 5</li>
        <li id="post-6">Item 6</li>
    </ul>
    <button id="addLi">添加一个li</button>
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        li.innerHTML = 'Item new';
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